Are you thinking about breathing? There’s something called the 7/11 breathing technique that can help with hyperventilating. It’s basically counting to 7 as you breath in and 11 as you breath out, the idea being that if forces you to breath out more than you breath in, thus rebalancing the oxygen/CO2 levels.

Doesn’t matter exactly about the numbers, just so long as ‘out’ breath is longer than the ‘in’ breath.